Next story in Space

The upcoming Geminid meteor shower next week may promise to be the best sky show of the year, but for many scientists it's a space light show shrouded in mystery.

Skywatchers should catch a nice view of the beguiling phenomenon between local midnight and sunrise on Tuesday, Dec. 14.

Most meteor showers come from comets, which spew ample meteoroids for a night of shooting stars. The Geminids are different. Their source is not a comet but a strange rocky object named 3200 Phaethon that sheds very little dusty debris not nearly enough to explain the Geminids.

"The Geminids are my favorite, because they defy explanation," said NASA astronomer Bill Cooke, a meteor expert at the agency's Marshall Space Flight Center in Huntsville, Ala.

This sky map shows where to look to see the Geminid meteor shower when the peak on Dec. 13 and Dec. 14.

Geminids meteor mystery
Meteor showers are created when the Earth passes through a stream of small space rocks, which then burn up as they pass through the atmosphere, creating so-called " shooting stars." But astronomers still don't know where all the rocky material for the Geminid shower comes from.

"Of all the debris streams Earth passes through every year, the Geminids' is by far the most massive," Cooke said in a statement. "When we add up the amount of dust in the Geminid stream, it outweighs other streams by factors of 5 to 500."

This makes the Geminids the gorilla of meteor showers. Yet 3200 Phaethon is more of a weakling.

3200 Phaethon was discovered in 1983 by NASA's IRAS satellite and promptly classified as an asteroid.

After all, scientists thought, what else could the space object be? It did not have a tail, its orbit intersected the main asteroid belt and its colors strongly resembled that of other asteroids. In fact, 3200 Phaethon resembles main belt asteroid Pallas so much, it might be a small chip off that massive block, NASA officials said.

"If 3200 Phaethon broke apart from asteroid Pallas, as some researchers believe, then Geminid meteoroids might be debris from the breakup," Cooke said. "But that doesn't agree with other things we know."

Science editor Alan Boyle's blog: "Astronaut Abby" is at the controls of a social-media machine that is launching the 15-year-old from Minnesota to Kazakhstan this month for the liftoff of the International Space Station's next crew.

Those "other things" includes the orbits of the Geminid meteoroids, which suggest they were ejected from 3200 Phaethon when the object was close to the sunnot when it was out in the asteroid belt in a cosmic break-up with Pallas.

The term meteoroid refers to space rocks that have not yet entered Earth's atmosphere to become a blazing fireball, or meteor. If any of these objects reach the ground, they are called meteorites.

Some scientists, on the other hand, think that the debris feeding the Geminids is created when 3200 Phaethon swings in near the sun and receives a blast of solar heating that might boil jets of dust into the Geminid stream.

To test the hypothesis, researchers turned to NASA's twin STEREO spacecraft, which are designed to study solar activity. Coronagraphs onboard STEREO can detect sungrazing asteroids and comets, and in June 2009 they detected 3200 Phaethon only 15 solar diameters from the sun's surface.

The answer may surprise you
What happened next surprised David Jewitt and Jing Li, planetary scientists at the University of California at Los Angeles who analyzed the data.

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"3200 Phaethon unexpectedly brightened by a factor of two," they wrote. "The most likely explanation is that Phaethon ejected dust, perhaps in response to a break-down of surface rocks (through thermal fracture and decomposition cracking of hydrated minerals) in the intense heat of the sun."

Jewett and Li's hypothesis is compelling, but they point out a problem: The amount of dust 3200 Phaethon ejected during its 2009 sun encounter added a mere 0.01 percent to the mass of the Geminid debris stream not nearly enough to keep the stream replenished over time. Perhaps the rock comet was more active in the past?

"We just don't know," Cooke said. "Every new thing we learn about the Geminids seems to deepen the mystery."

This month when Earth passes through the Geminid debris stream it will produce as many as 120 meteors per hour over dark-sky sites.

Southern stargazing

Stars, galaxies and nebulas dot the skies over the European Southern Observatory's La Silla Paranal Observatory in Chile, in a picture released on Jan. 7. This image also shows three of the four movable units that feed light into the Very Large Telescope Interferometer, the world's most advanced optical instrument. Combining to form one larger telescope, they are greater than the sum of their parts: They reveal details that would otherwise be visible only through a telescope as large as the distance between them.
(Y. Beletsky / ESO)
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A balloon's view

Cameras captured the Grandville High School RoboDawgs' balloon floating through Earth's upper atmosphere during its ascent on Dec. 28, 2013. The Grandville RoboDawgs’ first winter balloon launch reached an estimated altitude of 130,000 feet, or about 25 miles, according to coaches Mike Evele and Doug Hepfer. It skyrocketed past the team’s previous 100,000-feet record set in June. The RoboDawgs started with just one robotics team in 1998, but they've grown to support more than 30 teams at public schools in Grandville, Mich.
(Kyle Moroney / AP)
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Spacemen at work

Russian cosmonauts Oleg Kotov, right, and Sergey Ryazanskiy perform maintenance on the International Space Station on Jan. 27. During the six-hour, eight-minute spacewalk, Kotov and Ryazanskiy completed the installation of a pair of high-fidelity cameras that experienced connectivity issues during a Dec. 27 spacewalk. The cosmonauts also retrieved scientific gear outside the station's Russian segment.
(NASA)
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Special delivery

The International Space Station's Canadian-built robotic arm moves toward Orbital Sciences Corp.'s Cygnus autonomous cargo craft as it approaches the station for a Jan. 12 delivery. The mountains below are the southwestern Alps.
(NASA)
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Accidental art

A piece of art? A time-lapse photo? A flickering light show? At first glance, this image looks nothing like the images we're used to seeing from the Hubble Space Telescope. But it's a genuine Hubble frame that was released on Jan. 27. Hubble's team suspects that the telescope's Fine Guidance System locked onto a bad guide star, potentially a double star or binary. This caused an error in the tracking system, resulting in a remarkable picture of brightly colored stellar streaks. The prominent red streaks are from stars in the globular cluster NGC 288.
(NASA / ESA)
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Supersonic test flight

A camera looking back over Virgin Galactic's SpaceShipTwo's fuselage shows the rocket burn with a Mojave Desert vista in the background during a test flight of the rocket plane on Jan. 10. Cameras were mounted on the exterior of SpaceShipTwo as well as its carrier airplane, WhiteKnightTwo, to monitor the rocket engine's performance. The test was aimed at setting the stage for honest-to-goodness flights into outer space later this year, and eventual commercial space tours.

Red lagoon

The VLT Survey Telescope at the European Southern Observatory's Paranal Observatory in Chile captured this richly detailed new image of the Lagoon Nebula, released on Jan. 22. This giant cloud of gas and dust is creating intensely bright young stars, and is home to young stellar clusters. This image is a tiny part of just one of 11 public surveys of the sky now in progress using ESO telescopes.
(ESO/VPHAS team)
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Fire on the mountain

This image provided by NASA shows a satellite view of smoke from the Colby Fire, taken by the Multi-angle Imaging SpectroRadiometer aboard NASA's Terra spacecraft as it passed over Southern California on Jan. 16. The fire burned more than 1,863 acres and forced the evacuation of 3,700 people.
(NASA via AP)
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Where stars are born

An image captured by NASA's Spitzer Space Telescope shows the Orion Nebula, an immense stellar nursery some 1,500 light-years away. This false-color infrared view, released on Jan. 15, spans about 40 light-years across the region. The brightest portion of the nebula is centered on Orion's young, massive, hot stars, known as the Trapezium Cluster. But Spitzer also can detect stars still in the process of formation, seen here in red hues.
(NASA / JPL-Caltech)
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A long, long time ago...

This long-exposure picture from the Hubble Space Telescope, released Jan. 8, is the deepest image ever made of any cluster of galaxies. The cluster known as Abell 2744 appears in the foreground. It contains several hundred galaxies as they looked 3.5 billion years ago. Abell 2744 acts as a gravitational lens to warp space, brightening and magnifying images of nearly 3,000 distant background galaxies. The more distant galaxies appear as they did more than 12 billion years ago, not long after the Big Bang.
(NASA / NASA via AFP - Getty Images)
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Frosty halo

Sun dogs are bright spots that appear in the sky around the sun when light is refracted through ice crystals in the atmosphere. These sun dogs appeared on Jan. 5 amid brutally cold temperatures along Highway 83, north of Bismarck, N.D. The temperature was about 22 degrees below zero Fahrenheit, with a 50-below-zero wind chill.